The Therma-CELL Mosquito Repellent creates an odorless cell of protection that is up to 98% effective against mosquitoes and other biting insects. It operates on a single butane cartridge, which heats a repellent mat releasing allethrin, which is a synthetic copy of the natural repellent found in chrysanthemum flowers, covering a 225-square feet area (15ft x 15ft) for up to four hours per mat or 12 hours per refill kit.